Method And Apparatus For Allocating Radio Resources In A Mobile Radio Network

ABSTRACT

A method and apparatus for allocating radio resources to an elastic session in a cell in a CDMA network is presented. The method comprises allocating, to the elastic session, a radio resource share corresponding to a reduced transmission rate wherein the reduction in transmission rate corresponds to a peak transmission rate of the elastic session being slowed down by a first slowdown rate. The first slow down rate is determined in dependency of the transmission rate requirements of the ongoing sessions in the cell in a manner so that the radio resource share allocated is not lower than a radio resource share corresponding to the maximum transmission rate if a total amount of resources available for allocation to ongoing sessions in the cell is sufficient for all ongoing sessions to transmit at a respective peak transmission rate.

FIELD OF THE INVENTION

The present invention relates to mobile radio communication in general,and in particular to a method and apparatus for allocating radioresources in a mobile radio communication network operating according tothe principles of code division multiple access (CDMA).

BACKGROUND

The radio bandwidth allocated to a mobile radio network is limited. In amobile radio network, the number of ongoing calls and/or data transfersessions and the rate by which bits are transferred in the ongoingcalls/data transfer sessions are limited by the radio bandwidth that hasbeen allocated to the mobile radio network. Since radio bandwidth is ascarce resource, there is a need for utilizing the bandwidth allocatedto a mobile radio network as efficiently as possible.

In a mobile radio network operating according to the principles of CDMA,the maximum transmission capacity available in the network is tightlycoupled to the amount of interference in the air interface. By keepingthe transmission power of a session low, the interference experienced byother sessions will be low, and the impact of the session on the maximumavailable transmission capacity will be limited.

In E. Altman, “Capacity of Multi-Service Cellular Networks withTransmission-Rate Control: A Queuing Analysis”, ACM Mobicom '02,Atlanta, Ga., Sep. 23-28, 2002, it is shown that by reducing thetransmission rate of all best effort sessions in a CDMA network by aslowdown rate a, the capacity of the network increases, despite the factthat a slower transmission rate implies a longer holding time for eachsession (assuming that the same amount of information is transferredregardless of transmission rate).

SUMMARY

A problem to which the present invention relates is how to improve theutilization of the radio resources allocated to a mobile radio networkoperating according to the principles of code division multiple access.

This problem is addressed by a method of allocating radio resources toan elastic session transmitted over a radio interface between a radiobase station involved in a plurality of ongoing sessions and a mobilestation in a mobile radio network operating according to code divisionmultiple access. The method comprises:

-   -   allocating, to the elastic session, reduced radio resources        corresponding to a reduced transmission rate wherein the        reduction in transmission rate corresponds to a peak        transmission rate of the elastic session being slowed down by a        first slowdown rate; and    -   determining the first slow down rate in dependency of the        transmission rate requirements of the ongoing sessions in a        manner so that the radio resource share allocated is not lower        than a radio resource share corresponding to the maximum        transmission rate if a total amount of resources available for        the radio base station to allocate to ongoing sessions is        sufficient for all ongoing sessions to transmit at a respective        peak transmission rate.

By determining the first slow down rate in dependency of thetransmission rate requirements of the ongoing sessions in the mannerdescribed above, it is achieved that slow down of transmission rates canbe restricted to situations when slow down is necessary in order toincrease the capacity of the system. Slow down of elastic sessions willonly have to be performed to the extent necessary in order for theamount of radio resources utilised by the sessions to fall within thetotal amount of radio resources available for allocation to thesessions. When the amount of radio resources available for allocation tothe sessions involving the radio base station is sufficient for allsessions to transmit at their respective peak transmission rate, no slowdown will have to be performed.

Hence, the utilisation of the available radio resources is optimised.

In one aspect of the invention, the determining further comprisesensuring that the reduced transmission rate is not lower than a minimumtransmission rate of the elastic session. Hereby is achieved thatelastic sessions performing real time transmissions of data can beslowed down without risking that the slow down is performed to an extentwhere an unacceptable real time transmission rate is reached.

In one embodiment of the invention, in which the elastic session belongsto one of at least two session classes, the first slow down rate isdetermined in accordance with a priority policy according to whichdifferent session classes are given different priority and sessions of ahigher priority class are allocated radio resources corresponding to areduced transmission rate only if a reduction of transmission rate ofsessions of session classes of lower priority is not sufficient.

In this embodiment, it is possible to allow sessions of high priority totransmit at a high transmission rate even if the total amount ofresources available for the ongoing sessions is not sufficient for eachsession to transmit at its peak transmission rate.

In another embodiment, the first slow down rate is determined inaccordance with a priority policy according to which, if a total amountof resources available for allocation to sessions involving the radiobase station is not sufficient for each ongoing session to transmit atits peak transmission rate, the transmission rate of each ongoingsession is slowed down with a slow down rate.

In one aspect of the invention, the allocating of resources to theelastic session is performed upon an indication indicating that a totalamount of resources available for allocation to ongoing sessions is notsufficient for all ongoing sessions to operate at their respective peaktransmission rate. Hereby is achieved that an elastic session cantransmit at its peak transmission rate at least until the resourcesavailable for allocation to ongoing sessions is not sufficient

In another aspect of the invention, the allocating of resources to theelastic session is performed upon the entry of a new session involvingthe radio base station. The entry of a new session will change the totalamount of resources available for allocation, as well as the number ofongoing sessions, and an updating of the radio resource shares allocatedto ongoing sessions could advantageously be performed.

In yet another aspect of the invention, the allocating of resources tothe elastic session is performed in response to an indication indicatingthat a total amount of resources available for allocation to ongoingsessions involving the radio base station has changed. Hence, if theradio resources available for allocation to ongoing sessions is changed,the radio resource shares allocated to the ongoing sessions can beadjusted accordingly.

The problem is further addressed by a computer program operable toexecute the inventive method, a radio network node comprising a computerarrangement arranged to execute the inventive computer program, and amobile radio network comprising the inventive radio network node.

In one embodiment of the invention, a method of optimising theutilisation of radio resources available for allocation by a radio basestation to sessions upheld between the radio base station and mobilestations in a mobile radio network operating according to code divisionmultiple access is provided. This method comprises:

-   -   checking whether the radio resources available for allocation        are sufficient for all upheld sessions to transmit data at a        respective peak transmission rate;    -   if so, allocating to the upheld sessions a respective radio        resource share allowing transmission at least the respective        peak transmission rate; and if not,    -   allocating to at least one upheld elastic session a reduced        radio resource share allowing for transmission at a respective        reduced transmission rate corresponding to the respective peak        transmission rate having been slowed down by a respective slow        down rate; wherein    -   the at least one respective slow down rates is selected in a        manner so that the radio resource share allocated to the at        least one upheld elastic session allows for transmission at        least a minimum transmission rate of the elastic session and so        that the radio resources available for allocation are fully        utilised by the upheld sessions.

In this embodiment, the reduced radio resource share allocated to atleast one upheld session can be determined according to a number ofdifferent priority policies, as is further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 schematically illustrates a mobile radio network.

FIG. 2 a is a flowchart schematically illustrating a resource allocationprocedure in which some session classes are given higher priority thanother session classes.

FIG. 2 b is a flowchart illustrating some additional steps which couldbe included in the process of FIG. 2 a if no admission control isapplied in the mobile radio network.

FIG. 3 is a flowchart schematically illustrating another resourceallocation procedure in which no sessions are given priority over othersessions.

FIG. 4 is a signalling diagram illustrates signalling between a mobileradio network and mobile stations that are active within a cell uponexit of a session or entry of a new session in the cell.

FIG. 5 a illustrates numerical results of blocking probabilities vs.slowdown rate for a system of three different session classes in a cellwhere the slow down rate a is fixed.

FIG. 5 b illustrates numerical results of blocking probabilities vs.maximum slowdown rate in a cell where resource allocation is performedaccording to the embodiment of FIG. 2 a.

FIG. 5 c illustrates numerical results of blocking probabilities vs.maximum slowdown rate in a cell where the resource allocation isperformed according to the embodiment of FIG. 3.

Table 1 shows numerical values used in the calculations presented inFIGS. 5 a-c.

DETAILED DESCRIPTION

A schematic illustration of a mobile radio network 100 operatingaccording to the principles of code division multiple access (CDMA) isshown in FIG. 1. Mobile radio network 100 will in the following bereferred to as CDMA network 100. A CDMA network 100 generally comprisesa number of radio base stations 105, where each base station 105 servesa geographical area referred to as a cell 110. A base station 105typically comprises an antenna and a radio transceiver for communicatingwith mobile stations 125 in the cell 110 over a radio interface 130. Thebase station 105 is generally connected to a core network 135 via aradio network control node 140. The radio network control node 140typically comprises software and hardware for controlling the radio basestation 105. The radio network control node 140 is often referred to asa radio network controller (RNC) or a base station controller (BSC).

The radio interface 130 can typically be used for voice calls, as wellas for data transfer sessions. In the following, calls, as well as datatransfer sessions, will be referred to as sessions. Different sessionsin the same cell could involve communication between the same mobilestation 125 and a radio base station 105, or between different mobilestations 125 and the radio base station 105.

In a CDMA network 100, a base station 105 can simultaneously transmitdata relating to several ongoing sessions by use of the same radiofrequency band. However, in order to ensure that each ongoing sessionreceives sufficient quality of service, the power levels and thetransmission rates of the ongoing sessions are kept at a level so thatinterference effects resides below tolerable levels.

In a typical CDMA network 100, different sessions can be transmitted atdifferent transmission rates. Moreover, for some sessions, the rate bywhich bits are transmitted can vary during an ongoing session. Suchsessions can be referred to as elastic sessions. For other sessions, therate by which bits are transmitted is fixed, such as for circuitswitched fax sessions and calls where a mobile station 125 can onlytransmit and receive data at a specified transmission rate employingimplicit or explicit transmission rate control mechanisms.

Elastic sessions may be divided into two groups: So called best effortservices, i.e. non-real-time elastic session by which a fixed amount ofdata is to be transferred and for which a slow down will imply a longerholding time, and real-time elastic sessions, where the transmissionrate may be reduced at the expense of quality of service, and for whicha slow down will normally not imply a longer holding time. Examples ofnon-real-time elastic sessions are packet switched fax sessions and datatransfer sessions where data is transferred by use of the TCP protocol,USD (User Diagram Protocol), Datagram Congestion Control Protocol orsimilar protocols. Examples of real-time elastic sessions are callswhere a mobile station 125 uses a voice coder allowing a flexible voicecoding, such as an Adaptive Multirate (AMR) codec, and real-time datatransfer sessions wherein the transmission rate can be adapted, such ase.g. sessions by which video information is transferred by use of avideo codec that can adapt the transmission rate.

The capacity of a CDMA network 100 can be measured as the average numberof sessions receiving service at a given time with a given level ofquality. By slowing down the transmission rates of all ongoingnon-real-time elastic sessions in a cell by a fixed slow down rate a,the capacity of a CDMA cell 110 can increase, as is shown in E. Altman,“Capacity of Multi-Service Cellular Networks with Transmission-RateControl: A Queuing Analysis”, ACM Mobicom '02, Atlanta, Ga., Sep. 23-28,2002, hereby incorporated by reference. The slow down rate a is a factorby which the transmission rate of all sessions is slowed down. Althougheach elastic session in a CDMA network 100 which applies a fixed slowdown rate a is served at a lower transmission rate than if no slow downrate was applied, the number of ongoing sessions can increase, and thetotal amount of information that can be simultaneously transmitted bythe CDMA network 100 is increased.

An elastic session typically has a peak transmission rate, R_(peak),which is the maximum transmission rate at which the elastic session canoperate, and a minimum transmission rate, R_(min), which is the minimumtransmission rate at which the elastic session can operate. A group ofsessions which have the same peak transmission rate, R_(peak), and thesame minimum transmission rate, R_(min), as well as the same normalizedsignal energy per bit requirement, E/N₀, will hereinafter be referred toas a session class. E denotes the required received signal energy perbit for the receiving party to discern the information, and N₀ denotesthe noise spectral density.

At many times, the number of ongoing sessions in a CDMA network 100 islow enough for each elastic session to operate at its peak transmissionrate, R_(peak). Thus, in such instances, by slowing down of allnon-real-time elastic sessions by a fixed slow down rate a, the radioresources would not be utilized in an optimal way. Rather, since eachsession which has been slowed down by the fixed slowdown rate a willoften be active for a longer period of time than if no slow down hadbeen applied, in order to transmit the same amount of information, theradio bandwidth occupied by the session will be occupied for longer, andother mobile stations 125, which request the start of a session duringthe extra residency time of the ongoing sessions, may have to be turneddown or may not be served at the requested transmission rate.

According to the invention, the slow down of a session in a cell 110 canbe made dependent on the required transmission rate of the other ongoingsessions in the cell 110. In other words, the allocation of resources toan elastic session served by a base station 105 is made in dependency ofthe resource requirements of the other ongoing sessions served by thebase station 105. Furthermore, according to the invention, the maximumpossible slow down of a session should advantageously be restricted sothat the resulting reduced transmission rate, R_(a), does not go belowthe minimum transmission rate, R_(min), of the session. Hence, a slowdown can successfully be applied to real-time elastic sessions as wellas to non-real-time elastic sessions.

The allocation of resources to an elastic session is preferably notstatic, but can advantageously be reviewed and updated. Such updatingcan e.g. take place upon the start of a new session served by the samebase station 105, upon handover between the same base station 105 andanother base station, and upon termination of another session served bythe same base station 105. By the inventive method, the total amount ofresources, C_(total), that are available for allocation to sessionswithin the cell 110 are distributed between ongoing sessions in a mannerso that the amount of resources allocated to a single session, andthereby also the overall resource utilization, is optimised inaccordance with a priority policy, as is further discussed below.

As mentioned above, the transmission rate by which information can betransmitted over a session depends on the transmission power of thesession, or, more correctly, on the power received by the receivingparty of the session. Let {tilde over (Δ)}(R) denote the minimum ratioof the received power and the total interference energy at the receivingparty that is required in order for a session to transmit at atransmission rate, R. {tilde over (Δ)} can then be expressed as:

$\begin{matrix}{{{\overset{\sim}{\Delta}(R)} = {\frac{E}{{WN}_{0}}R}},} & (1)\end{matrix}$

where E is the required received signal energy/bit for the session, N₀is the thermal noise density and W is the spread spectrum bandwidth. Inthe following, the minimum ratio {tilde over (Δ)}(R) required fortransmission at peak transmission rate, R_(peak), of will be denoted{tilde over (Δ)}_(peak).

Hence, the power P received by the base station 105 from a mobilestation 125 transmitting a session at transmission rate R must fulfilthe following relationship:

$\begin{matrix}{{\frac{P}{P_{noise} + I_{own} + I_{other} - P} = {\overset{\sim}{\Delta}(R)}},} & (2)\end{matrix}$

where P_(noise) is the background noise power, I_(own) is the totalpower received by base station 105 within its own cell 110, andI_(other) is the total power received by base station 105 from othercells 110.

By introducing the relationship

$\begin{matrix}{\Delta = \frac{\overset{\sim}{\Delta}}{1 + \overset{\sim}{\Delta}}} & (3)\end{matrix}$

equation (2) can be re-written as:

$\begin{matrix}{\frac{P}{P_{noise} + I_{own} + I_{other}} = {{\Delta (R)}.}} & (4)\end{matrix}$

Δ(R) is a measure of the share of the total resources allocated within acell 110 that are allocated to a session, and will in the following bereferred to as the resource share, Δ, of a session. If the resourceshare, Δ, allocated to a session is reduced, the maximum transmissionrate at which the session can transmit information is also reduced, asis clear from equations (1) and (3). The resource share Δ required for asession to transmit at peak transmission rate, R_(peak), will in thefollowing be referred to as the peak resource share, Δ_(peak), of thesession.

The slow down rate a, as mentioned above, can be defined as:

$\begin{matrix}{{a = \frac{R_{peak}}{R_{a}}},} & (5)\end{matrix}$

where R_(a) denotes the reduced transmission rate resulting from theslow down. Since R_(peak) varies between session classes, the reducedtransmission rate, R_(a), resulting from a slow down by the slow downrate a, will vary between session classes. Hence, the maximum slow downrate of a session, a_(max), corresponds to the minimum transmissionrate, R_(min) of the session.

From equations 1, 3 and 5, the following relation between A and a can bederived:

$\begin{matrix}{{a = \frac{\Delta_{peak}\left( {1 - \Delta_{a}} \right)}{\Delta_{a}\left( {1 - \Delta_{peak}} \right)}},} & (6)\end{matrix}$

where Δ_(a) denotes the resource share required by a sessiontransmitting at a reduced transmission rate R_(a), and will be referredto as the reduced resource share.

As can be seen from equation 1 and 3, the resource share Δ depends onthe required signal energy per bit, E. Since the required signal energyper bit often varies between session classes, the resource share Δrequired to transmit at a transmission rate R often vary between sessionclasses. Hence, in order to indicate the possible dependency of sessionclass, any resource share A will hereinafter be denoted Δ(k), where kdenotes a session class.

It is well known that a CDMA network 100 cannot operate beyond its polecapacity, which defines the theoretical maximum load of the system. Thepole capacity, C_(pole), can be defined as:

$\begin{matrix}{C_{pole} = \frac{1}{1 + \frac{I_{other}}{I_{own}}}} & (7)\end{matrix}$

In a cell 110 which supports sessions of K different session classes 1,. . . K, the total load Ω experienced by the cell 110 can be expressedas:

$\begin{matrix}{\Omega = {\sum\limits_{k = 1}^{K}\; {{M(k)}{\Delta (k)}}}} & (8)\end{matrix}$

where M(k) denotes the number of active sessions belonging to sessionclass k. In order to avoid total transmission failure within the cell110, the total load Ω must be kept below the pole capacity, C_(pole).

In the following, the total amount of radio resources available forallocation to sessions within a cell 110 will be referred to as thetotal amount of resources available for allocation, C_(total). As longas C_(total) is kept below the pole capacity, C_(pole), any measure ofC_(total) may be used. A CDMA system 100 often operates with a C_(total)well below the pole capacity.

In one embodiment of the invention, the allocation of radio resources inthe CDMA network 100 is made in accordance with a priority policy wheresome session classes are given higher priority than other sessionclasses. Hence, if the total amount of resources, C_(total), availablefor allocation to sessions served by a base station 105 is notsufficient for each session to operate at its peak transmission rate,R_(peak), sessions of lower priority will be slowed down first. Only ifthe slow down of the lower priority session classes is not sufficientwill slow down of the higher priority session classes be considered. Anexample of a method of allocating resources to sessions in thisembodiment is illustrated in FIG. 2, which will be further discussedbelow.

In another embodiment of the invention, the allocation of radioresources in the CDMA network 100 is made in accordance with a prioritypolicy where all elastic session classes are given the same priority.Hence, if the total amount of resources available for allocation tosessions served by a base station 105 is not sufficient for each sessionto operate at its peak transmission rate, R_(peak), all sessions areslowed down, but only as much as is necessary. However, the slow downrate, a, may vary between different session classes. An example of amethod of allocating radio resources to sessions in this embodiment isillustrated in FIG. 3, which will also be further discussed below.

In the embodiment of FIGS. 2 a and 2 b, some session classes k are givenhigher priority than other session classes. If the total amount ofresources available for allocation, C_(total), is not sufficient for allongoing sessions to transmit at their respective peak transmission rate,R_(peak), sessions of the lowest priority will be slowed down. Only ifthis slow down is not sufficient will sessions of the next lowestpriority be slowed down, and so forth. In the example of FIGS. 2 a and 2b, base station 105 supports K different session classes 1, . . . K,wherein session class K has lowest priority and session class 1 has thehighest priority.

The method illustrated in FIG. 2 a assumes that admission control isapplied in the CDMA system 100, so that a new session is only admittedif the total amount of radio resources, C_(total), is large enough foreach ongoing session to transmit at its minimum transmission rate,R_(min), or a higher transmission rate.

In step 200 of FIG. 2 a, a parameter representing the resourcesavailable for allocation, C, is given the value of C_(total). In step205 of FIG. 2 a, a counter N is set to a value representing the sessionclass having the lowest priority: K. In steps 215-225, the resourceshare of sessions of class k, Δ(k), is set to the peak resource share,Δ_(peak)(k), for session classes 1 to N−1. Δ_(peak)(k) is the requiredresources share per session of session class k required for supportingtransmission at the peak transmission rate, R_(peak)(k), of sessions ofsession class k. In step 210, a counter k is set to 1. In step 215, Δ(k)is set to Δ_(peak)(k). In step 220, the counter k is incremented by 1.In step 225, it is checked whether the value of counter k is equal tothe value of counter N. If not, step 215 is re-entered.

However, if the value of counter k has reached the value of N, then step230 is entered, in which a reduced share of resources, Δ_(a)(k), iscalculated for sessions of the Nth session class. This is done by addingthe resource shares, Δ, allocated to all sessions of session classes 1to N−1, and subtracting this sum from the total amount of resources,C_(total). The value thus obtained corresponds to the resource shareavailable to allocate to sessions of session class N. This value is thendivided by the number of sessions of session class N, M(N), in order toobtain the reduced resource share, Δ_(a)(N) of sessions of session classN.

Step 235 is then entered, in which the calculated reduced resource shareof session class N, Δ_(a)(N), is compared to the peak resource share,Δ_(peak)(N), of session class N. If this comparison shows that thereduced resource share, Δ_(a)(N), is larger than the peak resourceshare, Δ_(peak)(N), then step 240 is entered, in which the resourceshares allocated to sessions of session class (N), Δ(N), is set to thepeak resource share, Δ_(peak)(N). Hence, in this scenario, all sessionsare allocated their peak resource share, Δ_(peak), and all sessions cantransmit at their peak transmission rate, R_(peak). Step 295 is thenentered, in which the process ends.

However, if it is found in step 235 that the reduced resource share ofsession class N, Δ_(a)(N), is not larger than the peak resource share,Δ_(peak)(N), then step 245 is entered, in which the reduced resourceshare, Δ_(a)(N), is compared to the minimum resource share of sessionsof session class N, Δ_(min)(N). Δ_(min)(k) is the resource sharerequired for a session of session class k in order to supporttransmission at minimum transmission rate of session class k,R_(min)(k). If in step 245 it is found that the reduced resource share,Δ_(a)(N), is larger than or equal to the minimum resource share,Δ_(min)(N), then step 250 is entered, in which the resource share ofsessions of session class N, Δ(N), is set to the value of the reducedresource share of sessions of session class N, Δ_(a)(N). Hence, in thisscenario, all session classes but session class N can transmit at theirpeak transmission rate, R_(peak). The sessions of resource class N willbe slowed down by a slow down rate a(N), and will hence transmit at areduced transmission rate, R_(a)(N). Step 295 is then entered, in whichthe process ends.

However, if it is found in step 245 that the reduced resource share ofsessions of session class N, Δ_(a)(N), is smaller than the minimumresource share of sessions of session class N, Δ_(min)(N), then step 255is entered, in which the resource share allocated to sessions of sessionclass N, Δ(N), is set to the minimum resource share of session class N,Δ_(min)(N). In this scenario, the reduction of resources allocated tosessions of session class N to the minimum share of resources for thisclass is not sufficient, but a reduction of the resources allocated toat least one session class of a higher priority will also have to bemade. Hence, step 260 is then entered, in which the resources allocatedto sessions of session class N, i.e. M(N)Δ(N), is subtracted from theamount of resources available for allocation, C, in order to determinethe amount of resources available for allocation to the session classes1 to (N−1). Step 285 is then entered, in which the counter N is reducedby 1. In step 290, it is then checked whether the value of counter N islarger than 0, and if so, step 210 is re-entered, and the process isrepeated with a new value of N. If the check in step 290 finds that thevalue of counter N is zero, then the process ends in step 295.

One or more session classes supported by cell 110 of CDMA network 100may require a fixed transmission rate, as discussed above. If so, inorder to reduce the number of performed calculations, the resourcesrequired to support sessions of this fixed rate session class(es) can besubtracted from the amount of resources available for allocation, C, instep 200. Alternatively, such fixed rate session classes could betreated as an elastic session class of any priority, having the samevalue of Δ_(peak) and Δ_(min).

In a CDMA system 100 where a new/newly handed over session of a sessionclass of high priority is given higher priority than an ongoing sessionof lower priority, the admission control performed prior to performingthe method of FIG. 2 a, as discussed above, could be replaced by theadditional steps of the method of FIG. 2 a presented in FIG. 2 b. Step265 of FIG. 2 b can then be performed upon exit of step 260 of FIG. 2 a.In step 265, it is checked if the new value of C, i.e. the amount ofresources available to allocation to session classes of higher prioritythan N, is greater than zero. If not, the resource share, A, allocatedto session class N, is set to zero in step 270. In step 275, the counterK, representing the session class of the lowest priority for whichtransmission can be allowed, is reduced by 1, since the total amount ofresources is not sufficient to support transmission of all originalsession classes. Step 280 is then entered, in which the counter N is setto the value of K. Step 290 of FIG. 2 a is entered. However, if in step265 of FIG. 2 b it is found that the new value of C is larger than zero,then step 285 of FIG. 2 a is entered.

In an implementation of the invention in which the admission control ofFIG. 2 b is implemented, a check could be introduced, after all theclasses have been allocated their resource shares, Δ, as to whether anyof the allocated resource shares, A, have been set to zero. If so, itcould be checked whether there are any residual resources available. Ifso, these residual resources could be allocated to some of the sessionsof the session class for which Δ has been given the value zero.

In another embodiment of the invention, all elastic session classes aregiven the same priority. An example of a method of allocating radioresources to sessions in this embodiment is illustrated in FIG. 3. Themethod of FIG. 3 applies to the situation where the CDMA cell 110supports sessions of K different session classes, referred to as class1, . . . , K. The allocation of resources in such a cell 110 where allelastic session classes are given the same priority is not trivial,since the minimum and maximum transmission rates, R_(min) and R_(peak),may vary between classes, and it is possible that R_(min) of one classis greater than R_(peak) of another class.

In step 300, a counter k is given the value 1. In step 310, the amountof additional resources, C_(additional), which would be available if allsessions were to be allocated their minimum share of resources, Δ_(min)is determined according to

$C_{additonal} = {C_{total} - {\sum\limits_{j = 1}^{K}\; {{M(j)}{\Delta_{\min}(j)}}}}$

Step 315 is then entered, in which a reduced share of resources, Δ_(a),to be allocated to the sessions of session class k is determinedaccording to the following relation:

$\begin{matrix}{{{\Delta_{a}(k)} = {{\Delta_{\min}(k)} + {\frac{{M(k)}\left( {{\Delta_{peak}(k)} - {\Delta_{\min}(k)}} \right)}{\sum\limits_{j = 1}^{K}\; \left( {{M(j)}\left( {{\Delta_{peak}(j)} - {\Delta_{\min}(j)}} \right)} \right)}C_{additional}}}},} & (9)\end{matrix}$

so that the sessions of session class k are allocated a reduced resourceshare, Δ_(a)(k), corresponding to the minimum resources share,Δ_(min)(k), plus an additional resource share which is proportional tothe difference between the peak resource share, Δ_(peak)(k), and theminimum resource share, Δ_(min)(k), of session class k, as well as beingproportional to C_(additional).

In step 320, it is then checked whether the reduced resource share,Δ_(a)(k), allocated to sessions of session class k in step 315 is largerthan the peak resource share for sessions of session class k,Δ_(peak)(k). If so, step 325 is entered, in which the resource share,Δ(k) allocated to sessions of session class k is set to the peakresource share, Δ_(peak)(k). If not, step 330 is entered, in which it ischecked whether the counter k has reached the value K, i.e. if allsession classes have been allocated a resource share Δ. If so, theprocess is ended in step 340. If not, step 335 is entered, in which thecounter k is incremented by 1. Step 315 is then entered with a new valueof k, so that the allocated resource share, Δ(k), can be calculated fora new session class.

The method of FIG. 3 could include a step where it is checked, prior toentering step 315, whether the total amount of resources, C_(total), islarge enough for all admitted sessions to operate at their respectivepeak transmission rate, R_(peak). If so, the respective peak resourceshare, Δ_(peak)(k), could be allocated to all sessions of all sessionclasses, and the steps 315-335 would not have to be entered. In order toensure that the relation used in step 315 does not give rise to anycalculation problems, as would be the case if all ongoing sessions werefixed, the total amount of resources, C_(total), could preferably bereplaced, in FIG. 3, by the total amount of resources available tosessions of elastic classes. The total number of session classes, K,would then accordingly be replaced by the total number of elasticsession classes. The resources necessary for transmission in sessionsbelonging to classes of fixed transmission rate could advantageously beallocated to such sessions prior to entering step 300.

Steps 320 and 325 of FIG. 3 are not necessary but could be omitted.However, if omitted, sessions of a session class may sometimes transmitat a higher transmission power than is required for transmission at thepeak transmission rate of the session class, and hence causing anunnecessary high interference. Analogously, steps 235 and 240 could beomitted from the procedure illustrated in FIGS. 2 a and 2 b.

The resource allocating procedure of FIG. 3 calculates the resourceshare, Δ, to be allocated to a session of session class k when nosession class is given priority over any other session classes. Asimilar procedure could be used in an embodiment of the invention wheresessions are not grouped into session classes, but the resource share tobe allocated is calculated separately for each session. However, bygrouping the sessions into session classes and allocating the sameamount of resources to all sessions belonging to the same session class,the amount of resources to be allocated will only have to be determinedonce per session, and less calculations will have to be made within theCDMA system 100.

The priority policies employed in the procedures illustrated in FIGS. 2and 3, respectively, are examples only, and other priority policiescould be used for allocating radio resources to sessions in dependencyof the resource requirements of the other ongoing sessions in the cell110. For example, in an embodiment wherein some elastic session classesare given priority over other elastic session classes, different levelsof slow down can be applied, so that the slow down of the sessions in alow priority class is first made to a level so that the low priorityclass operates at a transmission rate lower than the peak transmissionrate, but higher than the minimum transmission rate. If further slowdown is required, sessions of higher priory classes can be somewhatslowed down, before the low priority class if further slowed down.Furthermore, the priority policy illustrated in FIG. 3 could be variedby introducing, to the second term on the right hand side of equation(9) used in step 315 of FIG. 3, a factor f(k) representing the priorityof the session class k:

$\begin{matrix}{{\Delta_{a}(k)} = {{\Delta_{\min}(k)} + {\frac{{M(k)}{f(k)}\left( {{\Delta_{peak}(k)} - {\Delta_{\min}(k)}} \right)}{\sum\limits_{j = 1}^{K}\; \left( {{M(j)}{f(k)}\left( {{\Delta_{peak}(j)} - {\Delta_{\min}(j)}} \right)} \right)}C_{additional}}}} & (10)\end{matrix}$

The allocation of resources to sessions served by a base station 105 canadvantageously be updated when the set up of a new session is requestedfrom base station 105, either by initiation of a new session or by asession being handed over to the base station 105. In addition, theallocation of resources to ongoing sessions could advantageously beupdated when a session served by base station 105 is terminated. Theradio resources in a cell 110 will hence be optimally utilised at anytime, and the resource share, Δ, allocated to a session within a cell110 will at any time be based on the requirements of the other presentlyongoing sessions within the cell 110.

The total amount of resources available for allocation, C_(total), oftendepends on the ongoing sessions in neighbouring cells 110, served byother base stations 105, (cf. equation 7). The total amounted ofresources available for allocation, C_(total), could be advantageouslybe updated at regular intervals, and the allocation of resources toongoing sessions could be updated upon such updating of C_(total), sothat any changes to C_(total) can be accounted for in the allocation ofresources.

As discussed above, the inventive method of sharing resources betweenelastic sessions can advantageously be applied in a CDMA network 100.Hardware and software for performing the allocation of resources independency of the resource requirements of ongoing sessions canadvantageously be part of the radio network control node 140, or of acorresponding central node. Alternatively, hardware and software forperforming the inventive method of allocating resources can be part ofthe radio base station 105.

Furthermore, the CDMA network 100 would preferably comprise hardware andsoftware for transmitting information signals, relating to theallocation of resources, between a mobile station 125 and the CDMAnetwork 100. In the following, it will be assumed that such signallinghardware and software, as well as the functionality for performing theresource allocation according to the invention, is implemented in theradio network control node 140. Needless to say, these functionalitiescould be implemented elsewhere in mobile radio system 100.

FIG. 4 a illustrates a scenario where initially four mobile stations,125 a, 125 b, 125 c, and 125 d uphold ongoing sessions in a cell 110controlled by a radio network control node 140. A fifth mobile station,mobile station 125 e, sends a session request 400 to start a session ofsession class k. Radio network control node 140 then calculates theresource share A to be allocated to the mobile station 125 e, based onthe available resources in the cell 110 as well as the resourcerequirements of the sessions of mobile stations 125 a-125 e, asdiscussed above in relation to FIGS. 2 and 3. Since the arrival of a newsession upheld by mobile station 125 e may alter the resource share thatshould be allocated to one or more of mobile stations 125 a-d, radionetwork control node 140 further re-calculates the resource sharesallocated to mobile stations 125 a, 125 b, 125 c and 125 d, as discussedin relation to FIGS. 2 and 3. The new resource shares allocated tosessions of mobile stations 125 a-125 e are then communicated to mobilestations 125 a-125 e in allocation messages 405 a-405 e, respectively.However, if no changes are necessary to the resource share allocated toa session of a mobile station 125, the corresponding allocation message405 does not have to be transmitted.

FIG. 4 b. illustrates the scenario when five mobile stations 125 a-125 eare initially upholding sessions in a cell 110. Mobile station 125 cthen terminates its session and transmits a termination request 410 tothe mobile radio network 100. The radio network control node 140 istriggered by the termination request 410 to update the radio resourceallocation to the ongoing sessions upheld by mobile stations 125 a, 125b, 125 d and 125 e, by executing a resource allocation procedure whichtakes into account the requirements of the other ongoing sessions, e.g.one of the resource allocation procedures illustrated in FIGS. 2 and 3.The new resource shares allocated to mobile stations 125 a, 125 b, 125 dand 125 e are then communicated to these mobile stations in messages 405a, 405 b, 405 d and 405 e, respectively.

In some instances, a session may leave the cell 110 without the mobilestation 125 a sending a termination request 410. This could e.g. be thecase when mobile station 125 a enters a geographical area of poor radiocoverage, or when the session is handed over to a different cell 110.Obviously, the resource allocation procedure could be initiated upon thedetection of a session having left the cell 110, regardless of whether atermination request 410 has been received by the mobile radio system 100or not.

In one embodiment of the invention, the resource allocation procedure isonly executed upon entry of a new session into the cell 110, and notupon exit of a session.

The session request 400 should preferably comprise information fromwhich the minimum and peak transmission rates, R_(min) and R_(peak), ofthe requested session are derivable. Such information could e.g. beinformation on the session class k to which the requested sessionbelongs, or information on R_(min) and R_(peak).

An allocation message 405 could e.g. comprise information on theallocated resources as a resource share Δ, as a transmission rate R, asa slowdown rate a, or as a transmission power P. The relationshipbetween these measures is given by equations 4-6 above. Although theresource share Δ discussed in the above relates to the power receivedfrom a mobile station 125 at the base station 105, the correspondingtransmission power to be used by the mobile station 125 can be obtainedby the mobile station 125 by measuring the received power on thedownlink channel and comparing the received power to the actual powertransmitted by the base station 105, if it is assumed that the path losson the uplink and the downlink are the same. The message 405 e,transmitted to the mobile station 125 e requesting a new session, couldbe the same as the allocation messages 405 a-405 d, communicating achange in the allocation of resources, or could be different.

In order to execute the inventive resource allocation procedure, theradio resource control node 140 would need access to information on thetotal amount of resources available for allocation, C_(total), and thenumber of ongoing sessions, M, in the cell 110, as well as the peak andminimum resource requirements of the ongoing sessions. This informationcould either be stored in the radio network control node 140 and beupdated from time to time, or be communicated from the base station 105each time the resource allocation procedure is to be executed.Furthermore, in a system which applies session classes, the radionetwork control node 140 would need access to information on the numberof session classes, K, supported by base station 105.

Although for the sake of simplicity of illustration the mobile stations125 a-125 e of FIGS. 4 a and 4 b are illustrated to uphold one sessioneach, two or more sessions could be upheld by the same mobile stations125. Updated resource shares allocated to two sessions upheld by thesame mobile station 125 could be communicated in one message 405, or inone message 405 per session.

By the present invention is achieved that at a light traffic load in acell of a mobile radio network, every ongoing session can operate at itspeak transmission rate. When the traffic load in the cell increases sothat every ongoing session cannot operate at its peak transmission rate,one or more of the ongoing sessions are slowed down to a transmissionrate below the peak transmission rate, but only to the extent that isnecessary. Hence, the utilization of radio resources of the mobile radionetwork can be optimised.

Although the above description mainly discusses the allocation of radioresources to session on the uplink channel, the method of allocatingradio resources can also be applied to the downlink channel. Whenapplying the method on the down link channel resource allocation, thetotal amount of resources available for allocation, C_(total), is notrestricted by the pole capacity, C_(pole), but rather by the totaltransmission power of the base station 105.

Numerical results show that the utilization of radio resources isgreatly improved by determining the slow down rates a in dependency fthe resource requirements of the ongoing sessions in the cell 110. InFIGS. 5 a-c, numerical results are shown obtained from studies of amodel of a cell 110 which applies admission control, and in whichsessions arrive according to a Poisson process of intensity λ with amean holding time of 1/μ The cell 110 used in the calculations supportssessions of three different session classes, which are referred to asclass 1 (FIXED), which is a fixed session class, class 2 (ELA 1) whichis an elastic session class, and class 3 (ELA 2) which is also anelastic session class. The numerical parameters of these session classesare given in Table 1, wherein Δ(2) represents the peak resource share ofsession class 2, Δ_(peak)(2), λ(2) is the arrival intensity of sessionclass 2, and â(2) represents the maximum slowdown rate of session class2, a_(max)(2), Δ(3) represents the peak resource share of session class3, etc. In the calculations presented in FIGS. 5 a-5 b, the numericalvalue of Δ in Table 1 is set of 0.049, the numerical value of λ is setto 29.26, and the numerical value of μ is set to 32.03 (which does notvary between session classes in the used cell model).

FIG. 5 a illustrates calculated blocking probabilities plotted as afunction of the slow down rate a of session class 3 for a system inwhich the slow down rates a of the elastic session classes do not dependon the transmission requirements of the ongoing sessions, but are fixedin all system states. Hence, the slow down rate of session classes 2 and3 is set to the maximum slow down rate, and calculations have beenperformed for six different slow down rates of session class 3:a(3)=a_(max)(3)=1, 2, 3, 4, 5 and 6. The case illustrated in FIG. 5 acorresponds to the allocation method disclosed in E. Altman, “Capacityof Multi-Service Cellular Networks with Transmission-Rate Control: AQueuing Analysis”, ACM Mobicom '02, Atlanta, Ga., Sep. 23-28, 2002. Theblocking probability is the probability of a new session arriving at thecell 110 being denied access by the admission control.

FIG. 5 b illustrates calculated blocking probabilities plotted as afunction of maximum slow down rate a_(max) of session class 3, for asystem in which the slow down rates a of the elastic session classes 2and 3, a(2) and a(3), are determined according to the resourcerequirements of the ongoing sessions according to the priority policyillustrated in FIG. 2 a. The maximum slow down rate of session class 2,a_(max)(2), is kept fixed, whereas calculations have been performed for6 different maximum slow down rates of session class 3: a_(max)(3)=1, 2,3, 4, 5 and 6.

FIG. 5 c illustrates the calculated blocking probabilities plotted as afunction of the maximum slow down rate a_(max) of session class 3, inthe case where the slow down rates a of the elastic session classes 2and 3, a(2) and a(3), are determined according to the resourcerequirements of the ongoing sessions according to the priority policyillustrated in FIG. 3. The maximum slow down rate of session class 2,a_(max)(2), is kept fixed, whereas calculations have been performed for6 different maximum slow down rates of session class 3: a_(max)(3)=1, 2,3, 4, 5 and 6.

It is clear from the diagrams of FIGS. 5 a-c that by employing aresource allocation method in which the slow down rate a of elasticsessions is determined in dependency of the resource requirements of theongoing sessions, the blocking probabilities are greatly reduced for allsession classes, and the utilization of radio resources is greatlyimproved. Further numerical results of the computations of theperformance of the inventive method will be published in Gabor Fodor andM. Telek, “Performance Analysis of the Uplink of a CDMA Cell SupportingElastic Services”, Conference proceedings of the 2005 IFIP NetworkingConference held at the University of Waterloo, Ontario, Canada, May 2-6,2005, hereby incorporated by reference.

One skilled in the art will appreciate that the present invention is notlimited to the embodiments disclosed in the accompanying drawings andthe foregoing detailed description, which are presented for purposes ofillustration only, but it can be implemented in a number of differentways, and it is defined by the following claims.

1. A method of allocating radio resources to an elastic sessiontransmitted over a radio interface between a radio base station involvedin a plurality of other ongoing sessions and a mobile station in amobile radio network operating according to code division multipleaccess, comprising allocating, to the elastic session, a radio resourceshare corresponding to a reduced transmission rate wherein the reductionin transmission rate corresponds to a peak transmission rate of theelastic session being slowed down by a first slowdown rate, the methodcharacterised by determining the first slow down rate in dependency ofthe transmission rate requirements of the ongoing sessions in a mannerso that the radio resource share allocated is not lower than a radioresource share corresponding to the maximum transmission rate if a totalamount of resources available for the radio base station to allocate toongoing sessions is sufficient for all ongoing sessions to transmit at arespective peak transmission rate.
 2. The method of claim 1, wherein thedetermining further comprises ensuring that the reduced transmissionrate is not lower than a minimum transmission rate of the elasticsession.
 3. The method of claim 2, wherein the elastic session is areal-time session.
 4. The method of claim 1, wherein the elastic sessionbelongs to one of at least two session classes; and the first slow downrate is determined in accordance with a priority policy according towhich different session classes are given different priority andsessions of a higher priority class are allocated radio resourcescorresponding to a reduced transmission rate only if a reduction oftransmission rate of sessions of session classes of lower priority isnot sufficient.
 5. The method of claim 1, wherein the first slow downrate is determined in accordance with a priority policy according towhich, if a total amount of resources available for allocation tosessions involving the radio base station is not sufficient for eachongoing session to transmit at its peak transmission rate, thetransmission rate of each ongoing session is slowed down with a slowdown rate.
 6. The method of claim 1, wherein each ongoing session isassociated with a peak transmission rate; and the allocating ofresources to the elastic session is performed upon an indicationindicating that a total amount of resources available for allocating toongoing sessions is not sufficient for all ongoing sessions to operateat their respective peak transmission rate.
 7. The method of claim 1,wherein the allocating of resources to the elastic session is performedupon the entry of a new session involving the radio base station.
 8. Themethod of claim 1, wherein the allocating of resources to the elasticsession is performed upon the exit of an ongoing session.
 9. The methodof claim 1, wherein the allocating of resources to the elastic sessionis performed in response to an indication indicating that a total amountof resources available for allocation to ongoing sessions involving theradio base station has changed.
 10. A computer program productcomprising: computer program code means operable to, when run on acomputer, execute the method of claim
 1. 11. A radio network node forallocating radio resources to sessions in a mobile radio networkoperating according to code division multiple access, the radio networknode comprising: a computer arrangement arranged to execute the computerprogram product of claim
 10. 12. A mobile radio network operatingaccording to code division multiple access comprising the radio networknode of claim 11.